Internet DRAFT - draft-templin-ironbis
draft-templin-ironbis
Network Working Group F. Templin, Ed.
Internet-Draft Boeing Research & Technology
Obsoletes: RFC6179 (if approved) March 28, 2014
Intended status: Informational
Expires: September 29, 2014
The Interior Routing Overlay Network (IRON)
draft-templin-ironbis-16.txt
Abstract
Since large-scale Internetworks such as the public Internet must
continue to support escalating growth due to increasing demand, it is
clear that Autonomous Systems (ASes) must avoid injecting excessive
de-aggregated prefixes into the interdomain routing system and
instead mitigate de-aggregation internally. This document describes
an Interior Routing Overlay Network (IRON) architecture that supports
sustainable growth within AS-interior routing domains while requiring
no changes to end systems and no changes to the exterior routing
system. In addition to routing scaling, IRON further addresses other
important issues including mobility management, mobile networks,
multihoming, traffic engineering, NAT traversal and security. While
business considerations are an important determining factor for
widespread adoption, they are out of scope for this document.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on September 29, 2014.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Differences With RFC6179 . . . . . . . . . . . . . . . . . . . 5
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. The Interior Routing Overlay Network . . . . . . . . . . . . . 8
4.1. IRON Client . . . . . . . . . . . . . . . . . . . . . . . 9
4.2. IRON Serving Router . . . . . . . . . . . . . . . . . . . 10
4.3. IRON Relay Router . . . . . . . . . . . . . . . . . . . . 10
5. IRON Organizational Principles . . . . . . . . . . . . . . . . 11
6. IRON Control Plane Operation . . . . . . . . . . . . . . . . . 13
6.1. IRON Client Operation . . . . . . . . . . . . . . . . . . 13
6.2. IRON Server Operation . . . . . . . . . . . . . . . . . . 14
6.3. IRON Relay Operation . . . . . . . . . . . . . . . . . . . 14
7. IRON Forwarding Plane Operation . . . . . . . . . . . . . . . 15
7.1. IRON Client Operation . . . . . . . . . . . . . . . . . . 15
7.2. IRON Server Operation . . . . . . . . . . . . . . . . . . 16
7.3. IRON Relay Operation . . . . . . . . . . . . . . . . . . . 17
8. IRON Reference Operating Scenarios . . . . . . . . . . . . . . 17
8.1. Both Hosts within Same IRON Instance . . . . . . . . . . . 17
8.1.1. EUNs Served by Same Server . . . . . . . . . . . . . . 17
8.1.2. EUNs Served by Different Servers . . . . . . . . . . . 19
8.1.3. Client-to-Client Tunneling . . . . . . . . . . . . . . 22
8.2. Mixed IRON and Non-IRON Hosts . . . . . . . . . . . . . . 23
8.2.1. From IRON Host A to Non-IRON Host B . . . . . . . . . 23
8.2.2. From Non-IRON Host B to IRON Host A . . . . . . . . . 25
8.3. Hosts within Different IRON Instances . . . . . . . . . . 26
9. Mobility, Multiple Interfaces, Multihoming, and Traffic
Engineering . . . . . . . . . . . . . . . . . . . . . . . . . 26
9.1. Mobility Management and Mobile Networks . . . . . . . . . 27
9.2. Multiple Interfaces and Multihoming . . . . . . . . . . . 27
9.3. Traffic Engineering . . . . . . . . . . . . . . . . . . . 28
10. Renumbering Considerations . . . . . . . . . . . . . . . . . . 28
11. NAT Traversal Considerations . . . . . . . . . . . . . . . . . 28
12. Multicast Considerations . . . . . . . . . . . . . . . . . . . 29
13. Nested EUN Considerations . . . . . . . . . . . . . . . . . . 29
13.1. Host A Sends Packets to Host Z . . . . . . . . . . . . . . 31
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13.2. Host Z Sends Packets to Host A . . . . . . . . . . . . . . 31
14. Implications for the Internet . . . . . . . . . . . . . . . . 32
15. Additional Considerations . . . . . . . . . . . . . . . . . . 33
16. Related Initiatives . . . . . . . . . . . . . . . . . . . . . 33
17. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 34
18. Security Considerations . . . . . . . . . . . . . . . . . . . 34
19. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 35
20. References . . . . . . . . . . . . . . . . . . . . . . . . . . 35
20.1. Normative References . . . . . . . . . . . . . . . . . . . 35
20.2. Informative References . . . . . . . . . . . . . . . . . . 36
Appendix A. IRON Operation over Internetworks with Different
Address Families . . . . . . . . . . . . . . . . . . 39
Appendix B. Scaling Considerations . . . . . . . . . . . . . . . 40
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 41
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1. Introduction
Growth in the number of prefix entries instantiated in the Internet
routing system has led to concerns regarding unsustainable routing
scaling [RFC4984][RADIR] [I-D.narten-radir-problem-statement].
Operational practices such as de-aggregation and the increased use of
multihoming with Provider-Independent (PI) addressing are resulting
in more and more prefixes being injected into the Internet routing
system. Furthermore, depletion of the public IPv4 address space has
raised concerns for both increased de-aggregation and an impending
address space run-out scenario. At the same time, the IPv6 routing
system is beginning to see growth [BGPMON] which must be managed in
order to avoid the same routing scaling issues the IPv4 Internet now
faces. Since the Internet must continue to scale to accommodate
increasing demand, it is clear that new methodologies and operational
practices for managing Autonomous System (AS) interior routing
systems are needed in order to avoid excessive routing scaling due to
de-aggregation.
These same issues apply also to Internetworks other than the public
Internet, including critical infrastructure networks such as
corporate enterprise networks, civil aviation networks, emergency
response networks, power grid networks, medical care networks, etc.
The architectural principles presented in this document therefore
apply equally to any such Internetwork.
Several related works have investigated routing scaling issues.
Virtual Aggregation (VA) [GROW-VA] and Aggregation in Increasing
Scopes (AIS) [EVOLUTION] are global routing proposals that introduce
routing overlays with Virtual Prefixes (VPs) to reduce the number of
entries required in each router's Forwarding Information Base (FIB)
and Routing Information Base (RIB). Routing and Addressing in
Networks with Global Enterprise Recursion (RANGER) [RFC5720] examines
recursive arrangements of enterprise networks that can apply to a
very broad set of use-case scenarios [RFC6139]. IRON specifically
adopts the RANGER Non-Broadcast, Multiple Access (NBMA) tunnel
virtual-interface model, and uses Asymmetric Extended Route
Optimization (AERO) [I-D.templin-aerolink] as its functional building
block. IRON further uses the Border Gateway Protocol (BGP) [RFC4271]
to coordinate mobility-related routing changes and uses the Dynamic
Host Configuration Protocol (DHCPv6) Prefix Delegation (PD) service
to delegate and register prefixes [RFC3633].
This document introduces an Interior Routing Overlay Network (IRON)
architecture with goals of supporting scalable routing and addressing
while requiring no changes to the Internetwork's interdomain routing
system. IRON observes the Internet Protocol standards
[RFC0791][RFC2460], while other network-layer protocols that can be
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encapsulated within IP packets (e.g., OSI/CLNP [RFC0994], etc.) are
also within scope.
IRON borrows concepts from VA and AIS, and further borrows concepts
from the Internet Vastly Improved Plumbing (Ivip) [IVIP-ARCH]
architecture proposal along with its associated Translating Tunnel
Router (TTR) mobility extensions [TTRMOB]. Indeed, the TTR model to
a great degree inspired the IRON mobility architecture design
discussed in this document. The Network Address Translator (NAT)
traversal techniques adapted for IRON were inspired by the Simple
Address Mapping for Premises Legacy Equipment (SAMPLE) proposal
[SAMPLE] [I-D.carpenter-softwire-sample] and by Teredo [RFC4380].
IRON is specifically adapted for Virtual Service Provider (VSP)
overlay networks that connect to the Internetwork as an AS and
service Aggregated Prefixes (APs) from which more-specific Client
Prefixes (CPs) are delegated. IRON is motivated by a growing end
user demand for mobility management, mobile networks, multihoming,
traffic engineering, NAT traversal and security while using stable
addressing to minimize dependence on network renumbering
[RFC4192][RFC5887]. IRON VSP overlay network instances use the
existing IPv4 and/or IPv6 Internetwork as virtual NBMA links for
tunneling inner network layer packets within outer network layer
headers (see Section 4). Each IRON instance requires deployment of a
small number of relays and servers in the Internetwork, as well as
client devices that connect End User Networks (EUNs). No
modifications to hosts, and no modifications to existing routers, are
required. The following sections discuss details of the IRON
architecture.
2. Differences With RFC6179
An earlier version of IRON was published as RFC6179. This version
clarifies that IRON operates at the intradomain level within an AS,
and is therefore not intended as an interdomain solution. IRON is
therefore complimentary with the approaches documented in interdomain
solutions such as the Identifier / Locator Network Protocol (ILNP)
[RFC6740] and the Locator I/D Split Protocol (LISP) [RFC6830]. This
version of IRON further introduces significant improvements in
security and route optimization, as well as a direct client-to-client
route optimization capability not found in RFC6179.
Some terminology has been changed for greater clarification,
including Virtual Service Provier (VSP), Aggregated Prefix (AP) and
Client Prefix (CP). This document further uses AERO
[I-D.templin-aerolink] as the primary route discovery mechanism. The
document finally adds a new section on renumbering considerations and
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adds enhanced security considerations.
3. Terminology
This document makes use of the following terms:
Aggregated Prefix (AP):
a short network-layer prefix (e.g., an IPv4 /16, an IPv6 /20, an
OSI Network Service Access Protocol (NSAP) prefix, etc.) that is
owned and managed by a Virtual Service Provider (VSP).
Client Prefix (CP):
a more-specific network-layer prefix (e.g., an IPv4 /28, an IPv6
/56, etc.) derived from an AP and delegated to a client end user
network.
Client Prefix Address (CPA):
a network-layer address belonging to a CP and assigned to an
interface in an End User Network (EUN).
End User Network (EUN):
an edge network that connects an end user's devices (e.g.,
computers, routers, printers, etc.) to the Internetwork. IRON
EUNs are mobile networks, and can change their ISP attachments
without having to renumber.
Interior Routing Overlay Network (IRON):
an AS-interior overlay network instance that appears as a virtual
enterprise network, and connects to the Internetwork the same as
for any AS.
IRON Client Router/Host ("Client"):
a customer device that logically connects EUNs to an IRON instance
via an NBMA tunnel virtual interface. The device is normally a
router, but may instead be a host if the "EUN" is a singleton end
system.
IRON Serving Router ("Server"):
a VSP's IRON instance router that provides forwarding and mapping
services for Clients.
IRON Relay Router ("Relay"):
a VSP's router that acts as a relay between the IRON instance and
the Internetwork.
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IRON Agent (IA):
generically refers to any of an IRON Client/Server/Relay.
IRON Instance:
a set of IRON Agents deployed by a VSP to service EUNs through
automatic tunneling over the Internetwork.
Internetwork Service Provider (ISP):
a service provider that connects an IA to the Internetwork. In
other words, an ISP is responsible for providing IAs with data
link services for basic connectivity.
Locator:
an IP address assigned to the interface of a router or end system
connected to a public or private network over which tunnels are
formed. Locators taken from public IP prefixes are routable on a
global basis, while locators taken from private IP prefixes
[RFC1918] are made public via Network Address Translation (NAT).
Routing and Addressing in Networks with Global Enterprise Recursion
(RANGER):
an architectural examination of virtual overlay networks applied
to enterprise network scenarios, with implications for a wider
variety of use cases.
Subnetwork Encapsulation and Adaptation Layer (SEAL):
an encapsulation sublayer that provides extended identification
fields and control messages to ensure deterministic network-layer
feedback.
Virtual Enterprise Traversal (VET):
a method for discovering border routers and forming dynamic tunnel
neighbor relationships over enterprise networks (or sites) with
varying properties.
Asymmetric Extended Route Optimization (AERO):
a means for a destination IA to securely inform a source IA of a
more direct path.
Virtual Service Provider (VSP):
a company that owns and manages a set of APs from which it
delegates CPs to EUNs.
VSP Overlay Network:
the same as defined above for IRON Instance.
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4. The Interior Routing Overlay Network
The Interior Routing Overlay Network (IRON) operates at the AS level
and provides a number of important services to End User Networks
(EUNs) that are not well supported in the current architecture,
including routing scaling, mobility management, mobile networks,
multihoming, traffic engineering and NAT traversal. This is
accomplisehd through the establishment of IRON instances as overlays
configured over the underlying Internetwork.
Each IRON instance consists of IRON Agents (IAs) that automatically
tunnel the packets of end-to-end communication sessions within
encapsulating headers used for Internetwork routing. IAs use the
AERO [I-D.templin-aerolink] virtual NBMA link model to encapsulate
inner network-layer packets within outer network layer headers, as
shown in Figure 1.
+-------------------------+
| Outer headers with |
~ locator addresses ~
| (IPv4 or IPv6) |
+-------------------------+ +-------------------------+
| Inner Packet Header | --> | Inner Packet Header |
~ with CPA addresses ~ --> ~ with CPA addresses ~
| (IPv4, IPv6, OSI, etc.) | --> | (IPv4, IPv6, OSI, etc.) |
+-------------------------+ +-------------------------+
| | --> | |
~ Inner Packet Body ~ --> ~ Inner Packet Body ~
| | --> | |
+-------------------------+ +-------------------------+
Inner packet before Outer packet after
encapsulation encapsulation
Figure 1: Encapsulation of Inner Packets within Outer IP Headers
Each IRON instance comprises a set of IAs distributed throughout the
Internetwork to provide routing services for a set of Aggregated
Prefixes (APs). (The APs may be owned either by the VSP, or by an
enterprise network customer that hires the VSP to manage its APs.)
VSPs delegate sub-prefixes from APs, which they provide to end users
as Client Prefixes (CPs). In turn, end users assign CPs to Client
IAs which connect their End User Networks (EUNs) to the VSP IRON
instance.
VSPs may have no affiliation with the ISP networks from which end
users obtain their basic Internetwork connectivity. In that case,
the VSP can service its end users without the need to coordinate its
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activities with ISPs or other VSPs. Further details on VSP business
considerations are out of scope for this document.
IRON requires no changes to end systems or to existing routers.
Instead, IAs are deployed either as new platforms or as modifications
to existing platforms. IAs may be deployed incrementally without
disturbing the existing Internetwork routing system, and act as
waypoints (or "cairns") for navigating VSP overly networks. The
functional roles for IAs are described in the following sections.
4.1. IRON Client
An IRON Client (or, simply, "Client") is a router that logically
connects EUNs to the VSP's IRON instance via tunnels, as shown in
Figure 2. Clients obtain CPs from their VSPs and use them to number
subnets and interfaces within the EUNs.
Each Client connects to one or more Servers in the IRON instance
which serve as default routers. Clients also dynamically discover
better routes through the receipt of AERO redirection messages.
A Client can be deployed on the same physical platform that also
connects EUNs to the end user's ISPs, but it may also be deployed as
a separate router within the EUN. (This model applies even if the
EUN connects to the ISP via a Network Address Translator (NAT) -- see
Section 7.7). Finally, a Client may also be a simple end system that
connects a singleton EUN and exhibits the outward appearance of a
host.
.-.
,-( _)-.
+--------+ .-(_ (_ )-.
| Client |--(_ ISP )
+---+----+ `-(______)-'
| <= T \ .-.
.-. u \ ,-( _)-.
,-( _)-. n .-(_ (- )-.
.-(_ (_ )-. n (_ Internetwork )
(_ EUN ) e `-(______)-'
`-(______)-' l ___
| s => (:::)-.
+----+---+ .-(::::::::)
| Host | .-(::: IRON :::)-.
+--------+ (:::: Instance ::::)
`-(::::::::::::)-'
`-(::::::)-'
Figure 2: IRON Client Connecting EUN to IRON Instance
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4.2. IRON Serving Router
An IRON serving router (or, simply, "Server") is a VSP's router that
provides forwarding and mapping services within the IRON instance for
the CPs that have been delegated to end user Clients. In typical
deployments, a VSP will deploy many Servers for the IRON instance in
a globally distributed fashion (e.g., as depicted in Figure 3) around
the Internetwork so that Clients can discover those that are nearby.
+--------+ +--------+
| Boston | | Tokyo |
| Server | | Server |
+--+-----+ ++-------+
+--------+ \ /
| Seattle| \ ___ /
| Server | \ (:::)-. +--------+
+------+-+ .-(::::::::)------+ Paris |
\.-(::: IRON :::)-. | Server |
(:::: Instance ::::) +--------+
`-(::::::::::::)-'
+--------+ / `-(::::::)-' \ +--------+
| Moscow + | \--- + Sydney |
| Server | +----+---+ | Server |
+--------+ | Cairo | +--------+
| Server |
+--------+
Figure 3: IRON Server Global Distribution Example
Each Server acts as a tunnel-endpoint router. The Server forms
bidirectional tunnel neighbor relationships with each of its
dependent Clients, and can also serve as the unidirectional tunnel
neighbor egress for dynamically discovered visiting Clients. (The
Server can also form bidirectional tunnel neighbor relationships with
visiting Clients, e.g., if a symmetric security association is
necessary.) Each Server also forms bidirectional tunnel neighbor
relationships with a set of Relays that can forward packets from the
IRON instance out to the native Internetwork and vice versa, as
discussed in the next section.
4.3. IRON Relay Router
An IRON Relay Router (or, simply, "Relay") is a router that connects
the VSP's IRON instance to the rest of the Internetwork.
Each VSP configures one or more Relays that advertise the VSP's APs
into the IPv4 and/or IPv6 Internetwork routing systems. Each Relay
associates with the VSP's IRON instance Servers, e.g., via tunnel
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virtual links over the IRON instance, via a physical interconnect
such as an Ethernet cable, etc. The Relay role is depicted in
Figure 4.
.-.
,-( _)-.
.-(_ (_ )-.
(_ Internetwork )
`-(______)-' | +--------+
| |--| Server |
+----+---+ | +--------+
| Relay |----| +--------+
+--------+ |--| Server |
_|| | +--------+
(:::)-. (Physical Interconnects)
.-(::::::::)
+--------+ .-(::: IRON :::)-. +--------+
| Server |=(:::: Instance ::::)=| Server |
+--------+ `-(::::::::::::)-' +--------+
`-(::::::)-'
|| (Tunnels)
+--------+
| Server |
+--------+
Figure 4: IRON Relay Router Connecting IRON Instance to Native
Internet
5. IRON Organizational Principles
Each IRON instance represents a distinct "patch" on the underlying
Internetwork "quilt", where the patches are stitched together by
standard routing. When a new IRON instance is deployed, it becomes
yet another patch on the quilt and coordinates its internal routing
system independently of all other patches. Figure 5 depicts the
logical arrangement of Relays, Servers, and Clients in an IRON
instance.
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.-.
,-( _)-.
.-(_ (_ )-.
(_ Internetwork )
`-(______)-'
<------------ Relays ------------>
________________________
(::::::::::::::::::::::::)-.
.-(:::::::::::::::::::::::::::::)
.-(:::::::::::::::::::::::::::::::::)-.
(::::::::::: IRON Instance :::::::::::::)
`-(:::::::::::::::::::::::::::::::::)-'
`-(::::::::::::::::::::::::::::)-'
<------------ Servers ------------>
.-. .-. .-.
,-( _)-. ,-( _)-. ,-( _)-.
.-(_ (_ )-. .-(_ (_ )-. .-(_ (_ )-.
(__ ISP A _) (__ ISP B _) ... (__ ISP x _)
`-(______)-' `-(______)-' `-(______)-'
<----------- NATs ------------>
<----------- Clients and EUNs ----------->
Figure 5: IRON Organization
Each Relay advertises the IPv4 APs managed by the VSP into the IPv4
Internetwork routing system and advertises the IPv6 APs managed by
the VSP into the IPv6 Internetwork routing system. Relays will
therefore receive packets with CPA destination addresses sent by end
systems in the Internetwork and forward them to a Server that
connects the Client to which the corresponding CP has been delegated.
Finally, the IRON instance Relays maintain synchronization by running
interior BGP (iBGP) between themselves the same as for ordinary
Autonomous System Border Routers (ASBRs).
In a simple VSP overlay network arrangement, each Server can be
configured as an ASBR for a stub AS using a private ASN [RFC1930] to
peer with each IRON instance Relay the same as for an ordinary eBGP
neighbor. (The Server and Relay functions can instead be deployed
together on the same physical platform as a unified gateway.) Each
Server maintains a working set of dependent Clients for which it
caches CP-to-Client mappings in its forwarding table. Each Server
also, in turn, propagates the list of CPs in its working set to its
neighboring Relays via eBGP. Therefore, each Server only needs to
track the CPs for its current working set of dependent Clients, while
each Relay will maintain a full CP-to-Server forwarding table that
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represents reachability information for all CPs in the IRON instance.
Each Client obtains its basic Internetwork connectivity from ISPs,
and connects to Servers to attach its EUNs to the IRON instance.
Each EUN can further connect to the IRON instance via multiple
Clients as long as the Clients coordinate with one another, e.g., to
mitigate EUN partitions. Clients may additionaly use private
addresses behind one or several layers of NATs. Each Client
initially discovers a list of nearby Servers then forms a
bidirectional tunnel neighbor relationship with one or more Servers
through an initial DHCPv6 prefix delegation exchange followed by
periodic keepalives.
After a Client connects to Servers, it forwards initial outbound
packets from its EUNs by tunneling them to a Server, which may, in
turn, forward them to a nearby Relay within the IRON instance. The
Client may subsequently receive redirection messages informing it of
a more direct route through a different IA within the IRON instance
that serves the final destination EUN.
IRON can also be used to support APs of network-layer address
families that cannot be routed natively in the underlying
Internetwork (e.g., OSI/CLNP over the public Internet, IPv6 over
IPv4-only Internetworks, IPv4 over IPv6-only Internetworks, etc.).
Further details for the support of IRON APs of one address family
over Internetworks based on different address families are discussed
in Appendix A.
6. IRON Control Plane Operation
Each IRON instance supports routing through the control plane startup
and runtime dynamic routing operation of IAs. The following sub-
sections discuss control plane considerations for initializing and
maintaining the IRON instance routing system.
6.1. IRON Client Operation
Each Client obtains one or more CPs in a secured exchange with the
VSP as part of the initial end user registration. Upon startup, the
Client discovers a list of nearby VSP Servers via, e.g., a location
broker, a well known website, a static map, etc.
After the Client obtains a list of nearby Servers, it registers its
CPs ia one or more Servers using DHCPCv6 Prefix Delegation (PD). The
Client then configures default routes that list the Servers as next
hops on the tunnel virtual interface. The Client may subsequently
discover more-specific routes through receipt of redirection
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messages.
6.2. IRON Server Operation
In a simple VSP overlay network arrangement, each IRON Server is
provisioned with the locators for Relays within the IRON instance.
The Server is further configured as an ASBR for a stub AS and uses
eBGP with a private ASN to peer with each Relay.
Upon startup, the Server uses eBGP to announce the list of CPs it is
currently serving to the overlay network Relays. The Server then
actively listens for Clients that register their CPs as described in
Section 6.1. When a new Client connects, the Server uses eBGP to
announce the new CP routes to its neighboring Relays; when an
existing Client disconnects, the Server withdraws its CP
announcements. This process can often be accommodated through
standard eBGP router configurations, e.g., on routers that can
announce and withdraw prefixes based on kernel route additions and
deletions.
6.3. IRON Relay Operation
Each IRON Relay is provisioned with the list of APs that it will
serve, as well as the locators for Servers within the IRON instance.
The Relay is also provisioned with eBGP peerings with neighboring
ASes in the Internetwork -- the same as for any ASBR.
In a simple VSP overlay network arrangement, each Relay connects to
each Server via IRON instance-internal eBGP peerings for the purpose
of discovering CP-to-Server mappings, and connects to all other
Relays using iBGP either in a full mesh or using route reflectors.
(The Relay only uses iBGP to announce those prefixes it has learned
from AS peerings external to the IRON instance, however, since all
Relays will already discover all CPs in the IRON instance via their
eBGP peerings with Servers.) The Relay then engages in eBGP routing
exchanges with peer ASes in the IPv4 and/or IPv6 Internetworks the
same as for any ASBR.
After this initial synchronization procedure, the Relay advertises
the APs to its eBGP peers in the Internetwork. In particular, the
Relay advertises the IPv6 APs into the IPv6 interdomain routing
system and advertises the IPv4 APs into the IPv4 interdomain routing
system, but it does not advertise the full list of the IRON overlay's
CPs to any of its eBGP peers. The Relay further advertises "default"
via eBGP to its associated Servers, then engages in ordinary packet-
forwarding operations.
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7. IRON Forwarding Plane Operation
Following control plane initialization, IAs engage in the cooperative
process of receiving and forwarding packets. IAs forward
encapsulated packets over the IRON instance using the mechanisms of
AERO [I-D.templin-aerolink], while Relays additionally forward
packets to and from the native IPv6 and/or IPv4 Internetworks. IAs
also use AERO control messages to coordinate with other IAs,
including the process of sending and receiving redirection messages,
error messages, etc. Each IA operates as specified in the following
sub-sections.
7.1. IRON Client Operation
After connecting to Servers as specified in Section 6.1, the Client
registers its active ISP connections with each of its connected
Servers. Thereafter, the Client sends periodic beacons (e.g., AERO
Neighbor Solicitation (NS) messages) to the Server via each ISP
connection to maintain tunnel neighbor address mapping state. The
beacons should be sent at no more than 30 second intervals (subject
to a small random delay) so that state in NATs on the path as well as
on the Server itself is refreshed regularly. Although the Client may
connect via multiple ISPs (each represented by a different locator
address), the CP itself is used to represent the bidirectional
Client-to-Server tunnel neighbor association. The CP therefore names
this "bundle" of ISP connections.
If the Client ceases to receive acknowledgements from a Server via a
specific ISP connection, it marks the Server as unreachable from that
ISP. (The Client should also inform the Server of this outage via
one of its working ISP connections.) If the Client ceases to receive
acknowledgements from the Server via multiple ISP connections, it
disconnects from the failing Server and connects to a different
nearby Server. The act of disconnecting from old servers and
connecting to new servers will soon propagate the appropriate routing
information among the IRON instance's Relays.
When an end system in an EUN sends a flow of packets to a
correspondent in a different network, the packets are forwarded
through the EUN via normal routing until they reach the Client, which
then tunnels the initial packets to one of its connected Servers as
its default router. In particular, the Client encapsulates each
packet in outer headers with its locator as the source address and
the locator of the Server as the destination address.
The Client uses the mechanisms specified in AERO to encapsulate each
packet to be forwarded, and uses the AERO redirection procedures to
coordinate route optimization. The Client further accepts control
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messages from its Servers, including neighbor coordination exchanges,
indications of PMTU limitations, redirections and other control
messages. When the Client is redirected to a foreign Server that
serves a destination CP, it forms a unidirectional tunnel neighbor
association with the foreign Server as the new next hop toward the
CP. (The visiting Client can also form a bidirectional tunnel
neighbor association with the foreign Server, e.g., if a symmetric
security association is necessary.)
Note that Client-to-Client tunneling is also enabled when the foreign
Client has indicated its willingness to accept Client-to-Client
communications. In that case, the foreign Server can allow the final
destination Client to return the redirection message, which removes
the foreign Server from the fowarding path.
7.2. IRON Server Operation
After the Server associates with nearby Relays, it accepts Client
connections and authenticates the NS messages it receives from its
already-connected Clients. The Server discards any NS messages that
failed authentication, and responds to authentic NS messages by
returning signed Neighbor Advertisement (NA) messages.
When the Server receives an encapsulated data packet from one of its
dependent Clients, it uses normal longest-prefix-match rules to
locate a forwarding table entry that matches the packet's inner
destination address. The Server then re-encapsulates the packet
(i.e., it removes the outer header and replaces it with a new outer
header), sets the outer destination address to the locator address of
the next hop and forwards the packet to the next hop.
When the Server receives an encapsulated data packet from a visiting
Client, it locates a forwarding table entry that matches the packet's
inner destination address. If the destination does not correspond to
one of the Server's dependent Clients, the Server silently drops the
packet. Otherwise, the Server re-encapsulates the packet and
forwards it to the correct dependent Client. If the Client is in the
process of disconnecting (e.g., due to mobility), the Server also
returns a redirection message listing a NULL next hop to inform the
visiting Client that the dependent Client has moved.
When the Server receives an encapsulated data packet from a Relay, it
again locates a forwarding table entry that matches the packet's
inner destination. If the destination does not correspond to one of
the Server's dependent Clients, the Server drops the packet and sends
a destination unreachable message. Otherwise, the Server re-
encapsulates the packet and forwards it to the correct dependent
Client.
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7.3. IRON Relay Operation
After each Relay has synchronized its APs (see Section 6.3) it
advertises them in the IPv4 and/or IPv6 interdomain routing systems.
These APs will be represented as ordinary routing information in the
interdomain routing system, and any packets originating from the IPv4
or IPv6 Internetwork destined to an address covered by one of the APs
will be forwarded to one of the VSP's Relays.
When a Relay receives a packet from the Internetwork destined to a
CPA covered by one of its APs, it behaves as an ordinary IP router.
Specifically, the Relay looks in its forwarding table to discover a
locator of a Server that serves the CP covering the destination
address. The Relay then simply forwards the packet to the Server,
e.g., via encapsulation over a tunnel virtual link, via a physical
interconnect, etc.
When a Relay receives a packet from a Server destined to a CPA
serviced by a different Server, the Relay forwards the packet toward
the correct Server while also sending a "predirect" indication as the
initial leg in the AERO redirection procedure. When the target IA
returns a redirection message, the Relay proxies the message by re-
encapsulating it and forwarding it to the previous hop.
8. IRON Reference Operating Scenarios
The following sections discuss the IRON reference operating
scenarios.
8.1. Both Hosts within Same IRON Instance
When both hosts are within EUNs served by the same IRON instance, it
is sufficient to consider the scenario in a unidirectional fashion,
i.e., by tracing packet flows only in the forward direction from
source host to destination host. The reverse direction can be
considered separately and incurs the same considerations as for the
forward direction. The simplest case occurs when the EUNs that
service the source and destination hosts are connected to the same
server, while the general case occurs when the EUNs are connected to
different Servers. The two cases are discussed in the following
sections.
8.1.1. EUNs Served by Same Server
In this scenario, the packet flow from the source host is forwarded
through the EUN to the source's IRON Client. The Client then tunnels
the packets to the Server, which simply re-encapsulates and forwards
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the tunneled packets to the destination's Client. The destination's
Client then removes the packets from the tunnel and forwards them
over the EUN to the destination. Figure 6 depicts the sustained flow
of packets from Host A to Host B within EUNs serviced by the same
Server via a "hairpinned" route:
________________________________________
.-( )-.
.-( )-.
.-( )-.
.( ).
.( ).
.( +------------+ ).
( +===================>| Server(S) |=====================+ )
( // +------------+ \\ )
( // .-. .-. \\ )
( //,-( _)-. ,-( _)-\\ )
( .||_ (_ )-. .-(_ (_ ||. )
((_|| ISP A .) (__ ISP B ||_))
( ||-(______)-' `-(______)|| )
( || | | vv )
( +-----+-----+ +-----+-----+ )
| Client(A) | | Client(B) |
+-----+-----+ VSP IRON Instance +-----+-----+
^ | ( (Overlaid on the Native Interntwork) ) | |
| .-. .-( .-) .-. |
| ,-( _)-. .-(________________________)-. ,-( _)-. |
.|(_ (_ )-. .-(_ (_ )|
(_| EUN A ) (_ EUN B |)
|`-(______)-' `-(______)-|
| | Legend: | |
| +---+----+ ----> == Native +----+---+ |
+-| Host A | ====> == Tunnel | Host B |<+
+--------+ +--------+
Figure 6: Sustained Packet Flow via Hairpinned Route
With reference to Figure 6, Host A sends packets destined to Host B
via its network interface connected to EUN A. Routing within EUN A
will direct the packets to Client(A) as a default router for the EUN,
which then encapsulates them in outer headers with its locator
address as the outer source address, the locator address of Server(S)
as the outer destination address, and the identifying information
associated with its tunnel neighbor state as the identity. Client(A)
then simply forwards the encapsulated packets into the ISP network
connection that provided its locator. The ISP will forward the
encapsulated packets into the Internetwork without filtering since
the (outer) source address is topologically correct. Once the
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packets have been forwarded into the Internetwork, routing will
direct them to Server(S).
Server(S) will receive the encapsulated packets from Client(A) then
check its forwarding table to discover an entry that covers
destination address B with Client(B) as the next hop. Server(S) then
re-encapsulates the packets in a new outer header that uses the
source address, destination address, and identification parameters
associated with the tunnel neighbor state for Client(B). Server(S)
then forwards these re-encapsulated packets into the Internetwork,
where routing will direct them to Client(B). Client(B) will, in
turn, decapsulate the packets and forward the inner packets to Host B
via EUN B.
8.1.2. EUNs Served by Different Servers
In this scenario, the initial packets of a flow produced by a source
host within an EUN connected to the IRON instance by a Client must
flow through both the Server of the source host and a nearby Relay,
but route optimization can eliminate these elements from the path for
subsequent packets in the flow. Figure 7 shows the flow of initial
packets from Host A to Host B within EUNs of the same IRON instance:
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________________________________________
.-( )-.
.-( +------------+ )-.
.-( +======>| Relay(R) |=======+ )-.
.( || +*--*--*--*-*+ || ).
.( || * * vv ).
.( +--------++--+* *+--++--------+ ).
( +==>| Server(A) *| | Server(B) |====+ )
( // +----------*-+ +------------+ \\ )
( // .-. * .-. \\ )
( //,-( _)-. * ,-( _)-\\ )
( .||_ (_ )-. * .-(_ (_ ||. )
((_|| ISP A .) * (__ ISP B ||_))
( ||-(______)-' * `-(______)|| )
( || | * | vv )
( +-----+-----+ * +-----+-----+ )
| Client(A) |<* | Client(B) |
+-----+-----+ VSP IRON Instance +-----+-----+
^ | ( (Overlaid on the Native Internetwork) ) | |
| .-. .-( .-) .-. |
| ,-( _)-. .-(________________________)-. ,-( _)-. |
.|(_ (_ )-. .-(_ (_ )|
(_| EUN A ) (_ EUN B |)
|`-(______)-' `-(______)-|
| | Legend: | |
| +---+----+ ----> == Native +----+---+ |
+-| Host A | ====> == Tunnel | Host B |<+
+--------+ <**** == Redirect +--------+
Figure 7: Initial Packet Flow Before Redirects
With reference to Figure 7, Host A sends packets destined to Host B
via its network interface connected to EUN A. Routing within EUN A
will direct the packets to Client(A) as a default router for the EUN,
which then encapsulates them in outer headers that use the source
address, destination address, and identification parameters
associated with the tunnel neighbor state for Server(A). Client(A)
then forwards the encapsulated packets into the ISP network
connection that provided its locator, which will forward the
encapsulated packets into the Internetwork where routing will direct
them to Server(A).
Server(A) receives the encapsulated packets from Client(A) and
consults its forwarding table to determine that the most-specific
matching route is via Relay(R) as the next hop. Server(A) then re-
encapsulates the packets in outer headers that use the source
address, destination address, and identification parameters
associated with Relay (R), and forwards them into the Internetwork
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where routing will direct them to Relay(R). (Note that the Server
could instead forward the packets directly to the Relay without
encapsulation when the Relay is directly connected, e.g., via a
physical interconnect.)
Relay(R) receives the forwarded packets from Server(A) then checks
its forwarding table to discover a CP entry that covers inner
destination address B with Server(B) as the next hop. Relay(R) then
sends a "predirect" indication forward to Server(B) to inform the
server that a redirection message must be returned. Relay(R) finally
re-encapsulates the packets in outer headers that use the source
address, destination address, and identification parameters
associated with Server(B), then forwards them into the Internetwork
where routing will direct them to Server(B). (Note again that the
Relay could instead forward the packets directly to the Server, e.g.,
via a physical interconnect.)
Server(B) receives the "predirect" and forwarded packets from
Relay(R), then checks its forwarding table to discover a CP entry
that covers destination address B with Client(B) as the next hop.
Server(B) returns a redirection message to Relay(R), which proxies
the message back to Server(A), which then proxies the message back to
Client(A).
Server(B) then re-encapsulates the packets in outer headers that use
the source address, destination address, and identification
parameters associated with Client(B), then forwards them into the
Internetwork where routing will direct them to Client(B). Client(B)
will, in turn, decapsulate the packets and forward the inner packets
to Host B via EUN B.
After the initial flow of packets, Client(A) will have received one
or more redirection messages listing Server(B) as a better next hop,
and will establish unidirectional tunnel neighbor state listing
Server(B) as the next hop toward the CP that covers Host B. Client(A)
thereafter forwards its encapsulated packets directly to the locator
address of Server(B) without involving either Server(A) or Relay(B),
as shown in Figure 8.
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________________________________________
.-( )-.
.-( )-.
.-( )-.
.( ).
.( ).
.( +------------+ ).
( +====================================>| Server(B) |====+ )
( // +------------+ \\ )
( // .-. .-. \\ )
( //,-( _)-. ,-( _)-\\ )
( .||_ (_ )-. .-(_ (_ ||. )
((_|| ISP A .) (__ ISP B ||_))
( ||-(______)-' `-(______)|| )
( || | | vv )
( +-----+-----+ +-----+-----+ )
| Client(A) | | Client(B) |
+-----+-----+ IRON Instance +-----+-----+
^ | ( (Overlaid on the Native Internetwork) ) | |
| .-. .-( .-) .-. |
| ,-( _)-. .-(________________________)-. ,-( _)-. |
.|(_ (_ )-. .-(_ (_ )|
(_| EUN A ) (_ EUN B |)
|`-(______)-' `-(______)-|
| | Legend: | |
| +---+----+ ----> == Native +----+---+ |
+-| Host A | ====> == Tunnel | Host B |<+
+--------+ +--------+
Figure 8: Sustained Packet Flow After Redirects
8.1.3. Client-to-Client Tunneling
In the scenarios shown in Sections 8.1.1 and 8.1.2, if the foreign
Client has indicated its willingness to accept Client-to-Client
communications, then the foreign Server can allow the foreign Client
to return the redirection message, i.e., by passing the "predirect"
message on to the Client. In that case, the two Clients become peers
in either a unidirectional or bidirectional tunnel neighbor
relationship as shown in Figure 9:
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________________________________________
.-( )-.
.-( )-.
.-( )-.
.( ).
.( ).
.( ).
( +=======================================================+ )
( // \\ )
( // .-. .-. \\ )
( //,-( _)-. ,-( _)-\\ )
( .||_ (_ )-. .-(_ (_ ||. )
((_|| ISP A .) (__ ISP B ||_))
( ||-(______)-' `-(______)|| )
( || | | vv )
( +-----+-----+ +-----+-----+ )
| Client(A) | | Client(B) |
+-----+-----+ VSP IRON Instance +-----+-----+
^ | ( (Overlaid on the Native Internetwork) ) | |
| .-. .-( .-) .-. |
| ,-( _)-. .-(________________________)-. ,-( _)-. |
.|(_ (_ )-. .-(_ (_ )|
(_| EUN A ) (_ EUN B |)
|`-(______)-' `-(______)-|
| | Legend: | |
| +---+----+ <---> == Native +----+---+ |
+-| Host A | <===> == Tunnel | Host B |<+
+--------+ +--------+
Figure 9: Client-to-Client Tunneling
8.2. Mixed IRON and Non-IRON Hosts
The cases in which one host is within an IRON EUN and the other is in
a non-IRON EUN (i.e., one that connects to the native Internetwork
instead of the IRON) are described in the following sub-sections.
8.2.1. From IRON Host A to Non-IRON Host B
Figure 10 depicts the IRON reference operating scenario for packets
flowing from Host A in an IRON EUN to Host B in a non-IRON EUN.
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_________________________________________
.-( )-. )-.
.-( +-------)----+ )-.
.-( | Relay(A) |--------------------------+ )-.
.( +------------+ \ ).
.( +=======>| Server(A) | \ ).
.( // +--------)---+ \ ).
( // ) \ )
( // IRON ) \ )
( // .-. Instance ) .-. \ )
( //,-( _)-. ) ,-( _)-. \ )
( .||_ (_ )-. ) The Native .- _ (_ )-| )
( _|| ISP A ) ) Internetwork (_ ISP B |))
( ||-(______)-' ) `-(______)-' | )
( || | )-. | v )
( +-----+ ----+ )-. +-----+-----+ )
| Client(A) |)-. | Router(B) |
+-----+-----+ +-----+-----+
^ | ( ) | |
| .-. .-( .-) .-. |
| ,-( _)-. .-(________________________)-. ,-( _)-. |
.|(_ (_ )-. .-(_ (_ )|
(_| EUN A ) ( EUN B |)
|`-(______)-' `-(______)-|
| | Legend: | |
| +---+----+ ----> == Native +----+---+ |
+-| Host A | ====> == Tunnel | Host B |<+
+--------+ +--------+
Figure 10: From IRON Host A to Non-IRON Host B
In this scenario, Host A sends packets destined to Host B via its
network interface connected to IRON EUN A. Routing within EUN A will
direct the packets to Client(A) as a default router for the EUN,
which then encapsulates them and forwards them into the Internetwork
routing system where they will be directed to Server(A).
Server(A) receives the encapsulated packets from Client(A) then
forwards them to Relay(A), which simply forwards the unencapsulated
packets into the Internetwork. Once the packets are released into
the Internetwork, routing will direct them to the final destination
B. (Note that for simplicity Server(A) and Relay(A) are depicted in
Figure 10 as two concatenated "half-routers", and the forwarding
between the two halves is via encapsulation, via a physical
interconnect, via a shared memory operation when the two halves are
within the same physical platform, etc.)
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8.2.2. From Non-IRON Host B to IRON Host A
Figure 11 depicts the IRON reference operating scenario for packets
flowing from Host B in an Non-IRON EUN to Host A in an IRON EUN.
_________________________________________
.-( )-. )-.
.-( +-------)----+ )-.
.-( | Relay(A) |<-------------------------+ )-.
.( +------------+ \ ).
.( +========| Server(A) | \ ).
.( // +--------)---+ \ ).
( // ) \ )
( // IRON ) \ )
( // .-. Instance ) .-. \ )
( //,-( _)-. ) ,-( _)-. \ )
( .||_ (_ )-. ) The Native .- _ (_ )-| )
( _|| ISP A ) ) Internetwork (_ ISP B |))
( ||-(______)-' ) `-(______)-' | )
( vv | )-. | | )
( +-----+ ----+ )-. +-----+-----+ )
| Client(A) |)-. | Router(B) |
+-----+-----+ +-----+-----+
| | ( ) | |
| .-. .-( .-) .-. |
| ,-( _)-. .-(________________________)-. ,-( _)-. |
.|(_ (_ )-. .-(_ (_ )|
(_| EUN A ) ( EUN B |)
|`-(______)-' `-(______)-|
| | Legend: | |
| +---+----+ <---- == Native +----+---+ |
+>| Host A | <==== == Tunnel | Host B |-+
+--------+ +--------+
Figure 11: From Non-IRON Host B to IRON Host A
In this scenario, Host B sends packets destined to Host A via its
network interface connected to non-IRON EUN B. Interdomain routing
will direct the packets to Relay(A), which then forwards them to
Server(A).
Server(A) will then check its forwarding table to discover an entry
that covers destination address A with Client(A) as the next hop.
Server(A) then (re-)encapsulates the packets and forwards them into
the Internetwork, where routing will direct them to Client(A).
Client(A) will, in turn, decapsulate the packets and forward the
inner packets to Host A via its network interface connected to IRON
EUN A.
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8.3. Hosts within Different IRON Instances
Figure 12 depicts the IRON reference operating scenario for packets
flowing between Host A in an IRON instance A and Host B in a
different IRON instance B. In that case, forwarding between hosts A
and B always involves the Servers and Relays of both IRON instances,
i.e., the scenario is no different than if one of the hosts was
serviced by an IRON EUN and the other was serviced by a non-IRON EUN.
_________________________________________
.-( )-. .-( )-.
.-( +-------)----+ +---(--------+ )-.
.-( | Relay(A) | <---> | Relay(B) | )-.
.( +------------+ +------------+ ).
.( +=======>| Server(A) | | Server(B) |<======+ ).
.( // +--------)---+ +---(--------+ \\ ).
( // ) ( \\ )
( // IRON ) ( IRON \\ )
( // .-. Instance A ) ( Instance B .-. \\ )
( //,-( _)-. ) ( ,-( _). || )
( .||_ (_ )-. ) ( .-'_ (_ )|| )
( _|| ISP A ) ) ( (_ ISP B ||))
( ||-(______)-' ) ( '-(______)-|| )
( vv | )-. .-( | vv )
( +-----+ ----+ )-. .-( +-----+-----+ )
| Client(A) |)-. .-(| Client(B) |
+-----+-----+ The Native +-----+-----+
^ | ( Internetwork ) | ^
| .-. .-( .-) .-. |
| ,-( _)-. .-(________________________)-. ,-( _)-. |
.|(_ (_ )-. .-(_ (_ )|
(_| EUN A ) (_ EUN B |)
|`-(______)-' `-(______)-|
| | Legend: | |
| +---+----+ <---> == Native +----+---+ |
+>| Host A | <===> == Tunnel | Host B |<+
+--------+ +--------+
Figure 12: Hosts within Different IRON Instances
9. Mobility, Multiple Interfaces, Multihoming, and Traffic Engineering
While IRON Servers and Relays are typically arranged as fixed
infrastructure, Clients may need to move between different network
points of attachment, connect to multiple ISPs, or explicitly manage
their traffic flows. The following sections discuss mobility,
multihoming, and traffic engineering considerations for IRON Clients.
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9.1. Mobility Management and Mobile Networks
When a Client changes its network point of attachment (e.g., due to a
mobility event), it configures one or more new locators. If the
Client has not moved far away from its previous network point of
attachment, it simply informs its connected Server and any Client
neighbors of any locator changes sy sending an immediate NS message.
This operation is performance sensitive and should be conducted
immediately to avoid packet loss. This aspect of mobility can be
classified as a "localized mobility event".
If the Client has moved far away from its previous network point of
attachment, however, it re-issues the Server discovery procedure
described in Section 6.3. If the Client's current Server is no
longer close by, the Client may wish to move to a new Server in order
to reduce routing stretch. This operation is not performance
critical, and therefore can be conducted over a matter of minutes/
seconds instead of milliseconds/microseconds. This aspect of
mobility can be classified as a "global mobility event".
To move to a new Server, the Client first uses DHCPv6 PD to register
its CPs with the new Server, as described in Section 6.3. The Client
then uses DHCPv6 PD to inform its former Server that it has departed;
again, via a VSP-specific secured reliable transport connection. The
former Server will then withdraw its CP advertisements from the IRON
instance routing system and retain the (stale) forwarding table
entries until their lifetime expires. In the interim, the former
Server continues to deliver packets to the Client's last-known
locator addresses for the short term while informing any
unidirectional tunnel neighbors that the Client has moved.
Note that the Client may be either a mobile host or a mobile router.
In the case of a mobile router, the Client's EUN becomes a mobile
network, and can continue to use the Client's CPs without renumbering
even as it moves between different network attachment points.
9.2. Multiple Interfaces and Multihoming
A Client may register multiple ISP connections with each Server such
that multiple interfaces are naturally supported. This feature
results in the Client "harnessing" its multiple ISP connections into
a "bundle" that is represented as a single entity at the network
layer, and therefore allows for ISP independence at the link-layer.
A Client may further register with multiple Servers for fault
tolerance and reduced routing stretch. In that case, the Client
should register its full bundle of ISP connections with each of its
Servers unless it has a reason for carefully coordinating its
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individual ISP-to-Server mappings.
Client registration with multiple Servers results in "pseudo-
multihoming", in which the multiple homes are within the same VSP
IRON instance and hence share fate with the health of the IRON
instance itself.
9.3. Traffic Engineering
A Client can dynamically adjust its ISP-to-Server mappings in order
to influence inbound traffic flows. It can also change between
Servers when multiple Servers are available, but should strive for
stability in its Server selection in order to limit VSP network
routing churn.
A Client can select outgoing ISPs, e.g., based on current Quality-of-
Service (QoS) considerations such as minimizing delay or variance.
10. Renumbering Considerations
As new link-layer technologies and/or service models emerge, end
users will be motivated to select their basic Internetwork
connectivity solutions through healthy competition between ISPs. If
an end user's network-layer addresses are tied to a specific ISP,
however, they may be forced to undergo a painstaking renumbering even
if they wish to change to a different ISP [RFC4192][RFC5887].
When an end user Client obtains CPs from a VSP, it can change between
ISPs seamlessly and without need to renumber the CPs. IRON therefore
provides ISP independence at the link layer. If the end user is
later compelled to change to a different VSP, however, it would be
obliged to abandon its CPs and obtain new ones from the new VSP. In
that case, the Client would again be required to engage in a
painstaking renumbering event.
In order to avoid any future renumbering headaches, a Client that is
part of a cooperative collective (e.g., a large enterprise network)
could join together with the collective to obtain a suitably large PI
prefix then and hire a VSP to manage the prefix on behalf of the
collective. If the collective later decides to switch to a new VSP,
it simply revokes its PI prefix registration with the old VSP and
activates its registration with the new VSP.
11. NAT Traversal Considerations
The Internet today consists of a global public IPv4 routing and
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addressing system with non-IRON EUNs that use either public or
private IPv4 addressing. The latter class of EUNs connect to the
public Internet via Network Address Translators (NATs). When an IRON
Client is located behind a NAT, it selects Servers using the same
procedures as for Clients with public addresses and can then send NS
messages to Servers in order to get NA messages in return. The only
requirement is that the Client must configure its encapsulation
format to use a transport protocol that supports NAT traversal, e.g.,
UDP, TCP, etc.
Since the Server maintains state about its dependent Clients, it can
discover locator information for each Client by examining the
transport port number and IP address in the outer headers of the
Client's encapsulated packets. When there is a NAT in the path, the
transport port number and IP address in each encapsulated packet will
correspond to state in the NAT box and might not correspond to the
actual values assigned to the Client. The Server can then
encapsulate packets destined to hosts in the Client's EUN within
outer headers that use this IP address and transport port number.
The NAT box will receive the packets, translate the values in the
outer headers, then forward the packets to the Client. In this
sense, the Server's "locator" for the Client consists of the
concatenation of the IP address and transport port number.
In order to keep NAT and Server connection state alive, the Client
sends periodic NS beacons to the server to elicit an NA message from
the Server. IRON does not otherwise introduce any new complications
for NAT traversal or for applications embedding address referrals in
their payload.
12. Multicast Considerations
IRON Servers and Relays are topologically positioned to provide
Internet Group Management Protocol (IGMP) / Multicast Listener
Discovery (MLD) proxying for their Clients [RFC4605]. Further
multicast considerations for IRON (e.g., interactions with multicast
routing protocols, traffic scaling, etc.) are out of scope and will
be discussed in a future document.
13. Nested EUN Considerations
Each Client configures a locator that may be taken from an ordinary
non-CPA address assigned by an ISP or from a CPA address taken from a
CP assigned to another Client. In that case, the Client is said to
be "nested" within the EUN of another Client, and recursive nestings
of multiple layers of encapsulations may be necessary.
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For example, in the network scenario depicted in Figure 13, Client(A)
configures a locator CPA(B) taken from the CP assigned to EUN(B).
Client(B) in turn configures a locator CPA(C) taken from the CP
assigned to EUN(C). Finally, Client(C) configures a locator ISP(D)
taken from a non-CPA address delegated by an ordinary ISP(D).
Using this example, the "nested-IRON" case must be examined in which
a Host A, which configures the address CPA(A) within EUN(A),
exchanges packets with Host Z located elsewhere in a different IRON
instance EUN(Z).
.-.
ISP(D) ,-( _)-.
+-----------+ .-(_ (_ )-.
| Client(C) |--(_ ISP(D) )
+-----+-----+ `-(______)-'
| <= T \ .-.
.-. u \ ,-( _)-.
,-( _)-. n .-(_ (- )-.
.-(_ (_ )-. n (_ Internetwork )
(_ EUN(C) ) e `-(______)-'
`-(______)-' l ___
| CPA(C) s => (:::)-.
+-----+-----+ .-(::::::::)
| Client(B) | .-(: Multiple :)-. +-----------+
+-----+-----+ (:::::: IRON ::::::) | Relay(Z) |
| `-(: Instances:)-' +-----------+
.-. `-(::::::)-' +-----------+
,-( _)-. | Server(Z) |
.-(_ (_ )-. +---------------+ +-----------+
(_ EUN(B) ) |Relay/Server(C)| +-----------+
`-(______)-' +---------------+ | Client(Z) |
| CPA(B) +---------------+ +-----------+
+-----+-----+ |Relay/Server(B)| |
| Client(A) | +---------------+ .-.
+-----------+ +---------------+ ,-( _)-.
| |Relay/Server(A)| .-(_ (_ )-.
.-. +---------------+ (_ EUN(Z) )
,-( _)-. CPA(A) `-(______)-'
.-(_ (_ )-. +--------+ +--------+
(_ EUN(A) )---| Host A | | Host Z |
`-(______)-' +--------+ +--------+
Figure 13: Nested EUN Example
The two cases of Host A sending packets to Host Z, and Host Z sending
packets to Host A, must be considered separately, as described below.
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13.1. Host A Sends Packets to Host Z
Host A first forwards a packet with source address CPA(A) and
destination address Z into EUN(A). Routing within EUN(A) will direct
the packet to Client(A), which encapsulates it in an outer header
with CPA(B) as the outer source address and Server(A) as the outer
destination address then forwards the once-encapsulated packet into
EUN(B).
Routing within EUN(B) will direct the packet to Client(B), which
encapsulates it in an outer header with CPA(C) as the outer source
address and Server(B) as the outer destination address then forwards
the twice-encapsulated packet into EUN(C). Routing within EUN(C)
will direct the packet to Client(C), which encapsulates it in an
outer header with ISP(D) as the outer source address and Server(C) as
the outer destination address. Client(C) then sends this triple-
encapsulated packet into the ISP(D) network, where it will be routed
via the Internetwork to Server(C).
When Server(C) receives the triple-encapsulated packet, it forwards
it to Relay(C) which removes the outer layer of encapsulation and
forwards the resulting twice-encapsulated packet into the
Internetwork to Server(B). Next, Server(B) forwards the packet to
Relay(B) which removes the outer layer of encapsulation and forwards
the resulting once-encapsulated packet into the Internetwork to
Server(A). Next, Server(A) forwards the packet to Relay(A), which
decapsulates it and forwards the resulting inner packet via the
Internetwork to Relay(Z). Relay(Z), in turn, forwards the packet to
Server(Z), which encapsulates and forwards the packet to Client(Z),
which decapsulates it and forwards the inner packet to Host Z.
13.2. Host Z Sends Packets to Host A
When Host Z sends a packet to Host A, forwarding in EUN(Z) will
direct it to Client(Z), which encapsulates and forwards the packet to
Server(Z). Server(Z) will forward the packet to Relay(Z), which will
then decapsulate and forward the inner packet into the Internetwork.
Interdomain will convey the packet to Relay(A) as the next-hop
towards CPA(A), which then forwards it to Server(A).
Server (A) encapsulates the packet and forwards it to Relay(B) as the
next-hop towards CPA(B) (i.e., the locator for CPA(A)). Relay(B)
then forwards the packet to Server(B), which encapsulates it a second
time and forwards it to Relay(C) as the next-hop towards CPA(C)
(i.e., the locator for CPA(B)). Relay(C) then forwards the packet to
Server(C), which encapsulates it a third time and forwards it to
Client(C).
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Client(C) then decapsulates the packet and forwards the resulting
twice-encapsulated packet via EUN(C) to Client(B). Client(B) in turn
decapsulates the packet and forwards the resulting once-encapsulated
packet via EUN(B) to Client(A). Client(A) finally decapsulates and
forwards the inner packet to Host A.
14. Implications for the Internet
For IRON instances configured over the public Internet as the
underlying Internetwork, the IRON system requires a VSP deployment of
new routers/servers throughout the Internet to maintain well-balanced
virtual overlay networks. These routers/servers can be deployed
incrementally without disruption to existing Internet infrastructure
as long as they are appropriately managed to provide acceptable
service levels to end users.
End-to-end traffic that traverses an IRON instance may experience
delay variance between the initial packets and subsequent packets of
a flow. This is due to the IRON system allowing a longer path
stretch for initial packets followed by timely route optimizations to
utilize better next hop routers/servers for subsequent packets.
IRON instances work seamlessly with existing and emerging services
within the native Internet. In particular, end users serviced by an
IRON instance will receive the same service enjoyed by end users
serviced by non-IRON service providers. Internet services already
deployed within the native Internet also need not make any changes to
accommodate IRON end users.
The IRON system operates between IAs within the Internet and EUNs.
Within these networks, the underlying paths traversed by the virtual
overlay networks may comprise links that accommodate varying MTUs.
While the IRON system imposes an additional per-packet overhead that
may cause the size of packets to become slightly larger than the
underlying path can accommodate, IAs have a method for naturally
detecting and tuning out instances of path MTU underruns. In some
cases, these MTU underruns may need to be reported back to the
original hosts; however, the system will also allow for MTUs much
larger than those typically available in current Internet paths to be
discovered and utilized as more links with larger MTUs are deployed.
Finally, and perhaps most importantly, the IRON system provides in-
built mobility management, mobile networks, multihoming and traffic
engineering capabilities that allow end user devices and networks to
move about freely while both imparting minimal oscillations in the
routing system and maintaining generally shortest-path routes. This
mobility management is afforded through the very nature of the IRON
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service model, and therefore requires no adjunct mechanisms. The
mobility management and multihoming capabilities are further
supported by forward-path reachability detection that provides "hints
of forward progress" in the same spirit as for IPv6 Neighbor
Discovery (ND).
15. Additional Considerations
Considerations for the scalability of interdomain routing due to
multihoming, traffic engineering, and provider-independent addressing
are discussed in [RADIR] [I-D.narten-radir-problem-statement]. Other
scaling considerations specific to IRON are discussed in Appendix B.
Route optimization considerations for mobile networks are found in
[RFC5522].
In order to ensure acceptable end user service levels, the VSP should
conduct a capacity analysis and distribute sufficient Relays and
Servers for the IRON instance globally throughout the Internet. As
for common practices in the Internet today, such capacity analysis
can be conducted in parallel with actual deployment of the service.
16. Related Initiatives
IRON builds upon the concepts of the RANGER architecture [RFC5720] ,
and therefore inherits the same set of related initiatives. The
Internet Research Task Force (IRTF) Routing Research Group (RRG)
mentions IRON in its recommendation for a routing architecture
[RFC6115].
Virtual Aggregation (VA) [GROW-VA] and Aggregation in Increasing
Scopes (AIS) [EVOLUTION] provide the basis for the Virtual Prefix
concepts.
Internet Vastly Improved Plumbing (Ivip) [IVIP-ARCH] has contributed
valuable insights, including the use of real-time mapping. The use
of Servers as mobility anchor points is directly influenced by Ivip's
associated TTR mobility extensions [TTRMOB].
[RO-CR][I-D.bernardos-mext-nemo-ro-cr] discusses a route optimization
approach using a Correspondent Router (CR) model. The IRON Server
construct is similar to the CR concept described in this work;
however, the manner in which Clients coordinate with Servers is
different and based on the NBMA virtual link model popularized by
6over4 [RFC2529] and ISATAP [RFC5214].
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Numerous publications have proposed NAT traversal techniques. The
NAT traversal techniques adapted for IRON were inspired by the Simple
Address Mapping for Premises Legacy Equipment (SAMPLE) proposal
[SAMPLE][I-D.carpenter-softwire-sample].
The IRON Client-Server relationship is managed in essentially the
same way as for the Tunnel Broker model [RFC3053]. Numerous existing
provider networks that provide service similar to tunnel broker
(e.g., Hurricane Electric, SixXS, freenet6, etc.) provide existence
proofs that IRON-like overlay network services can be deployed and
managed on a global basis [BROKER].
IRON is further related to the Identifier-Locator Network Protocol
(ILNP) [RFC6740] and Locator / ID Split Protocol (LISP) [RFC6830]
proposals which address routing scaling aspects at the interdomain
level. IRON is therefore complimentary to these approaches.
17. IANA Considerations
There are no IANA considerations for this document.
18. Security Considerations
Security considerations that apply to tunneling in general are
discussed in [RFC6169].
The IRON system further depends on mutual authentication of IRON
Clients to Servers and Servers to Relays. As for all Internet
communications, the IRON system also depends on Relays acting with
integrity and not injecting false advertisements into the interdomain
routing system (e.g., to mount traffic siphoning attacks).
IRON Agents must perform message origin authentication on the packets
they accept from correspondents.
IRON Servers must ensure that any changes in a Client's locator
addresses are communicated only through an authenticated exchange
that is not subject to replay. For this reason, Clients periodically
send NS messages to the Server (using digital signatures if
necessary). Once the message has been authenticated, the Server
updates the Client's locator address to the new address.
Each IRON instance requires a means for assuring the integrity of the
interior routing system so that all Relays and Servers in the overlay
have a consistent view of CP<->Server bindings. Also, Denial-of-
Service (DoS) attacks on IRON Relays and Servers can occur when
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packets with spoofed source addresses arrive at high data rates.
However, this issue is no different than for any border router in the
public Internet today.
Middleboxes can interfere with tunneled packets within an IRON
instance in various ways. For example, a middlebox may alter a
packet's contents, change a packet's locator addresses, inject
spurious packets, replay old packets, etc. These issues are no
different than for middlebox interactions with ordinary Internet
communications. If man-in-the-middle attacks are a matter for
concern in certain deployments, however, IRON Agents can use IPsec
[RFC4301] or TLS/SSL [RFC5246] to protect the authenticity, integrity
and (if necessary) privacy of their tunneled packets.
19. Acknowledgements
The ideas behind this work have benefited greatly from discussions
with colleagues; some of which appear on the RRG and other IRTF/IETF
mailing lists. Robin Whittle and Steve Russert co-authored the TTR
mobility architecture, which strongly influenced IRON. Eric
Fleischman pointed out the opportunity to leverage anycast for
discovering topologically close Servers. Thomas Henderson
recommended a quantitative analysis of scaling properties.
The following individuals provided essential review input: Jari
Arkko, Mohamed Boucadair, Stewart Bryant, John Buford, Ralph Droms,
Wesley Eddy, Adrian Farrel, Dae Young Kim, and Robin Whittle.
Discussions with colleagues following the publication of RFC6179 have
provided useful insights that have resulted in significant
improvements to this, the Second Edition of IRON.
This document received substantial review input from the IESG and
IETF area directorates in the February 2013 timeframe. IESG members
and IETF area directorate representatives who contributed helpful
comments and suggestions are gratefully acknowledged.
20. References
20.1. Normative References
[I-D.templin-aerolink]
Templin, F., "Transmission of IPv6 Packets over AERO
Links", draft-templin-aerolink-10 (work in progress),
March 2014.
Templin Expires September 29, 2014 [Page 35]
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[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
September 1981.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
[RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
Host Configuration Protocol (DHCP) version 6", RFC 3633,
December 2003.
20.2. Informative References
[BGPMON] net, B., "BGPmon.net - Monitoring Your Prefixes,
http://bgpmon.net/stat.php", June 2010.
[BROKER] Wikipedia, W., "List of IPv6 Tunnel Brokers,
http://en.wikipedia.org/wiki/List_of_IPv6_tunnel_brokers",
August 2011.
[EVOLUTION]
Zhang, B., Zhang, L., and L. Wang, "Evolution Towards
Global Routing Scalability", Work in Progress,
October 2009.
[GROW-VA] Francis, P., Xu, X., Ballani, H., Jen, D., Raszuk, R., and
L. Zhang, "FIB Suppression with Virtual Aggregation", Work
in Progress, February 2011.
[I-D.bernardos-mext-nemo-ro-cr]
Bernardos, C., Calderon, M., and I. Soto, "Correspondent
Router based Route Optimisation for NEMO (CRON)",
draft-bernardos-mext-nemo-ro-cr-00 (work in progress),
July 2008.
[I-D.carpenter-softwire-sample]
Carpenter, B. and S. Jiang, "Legacy NAT Traversal for
IPv6: Simple Address Mapping for Premises Legacy Equipment
(SAMPLE)", draft-carpenter-softwire-sample-00 (work in
progress), June 2010.
[I-D.narten-radir-problem-statement]
Narten, T., "On the Scalability of Internet Routing",
draft-narten-radir-problem-statement-05 (work in
progress), February 2010.
[IVIP-ARCH]
Whittle, R., "Ivip (Internet Vastly Improved Plumbing)
Architecture", Work in Progress, March 2010.
Templin Expires September 29, 2014 [Page 36]
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[RADIR] Narten, T., "On the Scalability of Internet Routing", Work
in Progress, February 2010.
[RFC0994] International Organization for Standardization (ISO) and
American National Standards Institute (ANSI), "Final text
of DIS 8473, Protocol for Providing the Connectionless-
mode Network Service", RFC 994, March 1986.
[RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
E. Lear, "Address Allocation for Private Internets",
BCP 5, RFC 1918, February 1996.
[RFC1930] Hawkinson, J. and T. Bates, "Guidelines for creation,
selection, and registration of an Autonomous System (AS)",
BCP 6, RFC 1930, March 1996.
[RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4
Domains without Explicit Tunnels", RFC 2529, March 1999.
[RFC3053] Durand, A., Fasano, P., Guardini, I., and D. Lento, "IPv6
Tunnel Broker", RFC 3053, January 2001.
[RFC4192] Baker, F., Lear, E., and R. Droms, "Procedures for
Renumbering an IPv6 Network without a Flag Day", RFC 4192,
September 2005.
[RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
Protocol 4 (BGP-4)", RFC 4271, January 2006.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, December 2005.
[RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through
Network Address Translations (NATs)", RFC 4380,
February 2006.
[RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick,
"Internet Group Management Protocol (IGMP) / Multicast
Listener Discovery (MLD)-Based Multicast Forwarding
("IGMP/MLD Proxying")", RFC 4605, August 2006.
[RFC4984] Meyer, D., Zhang, L., and K. Fall, "Report from the IAB
Workshop on Routing and Addressing", RFC 4984,
September 2007.
[RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site
Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214,
March 2008.
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[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[RFC5522] Eddy, W., Ivancic, W., and T. Davis, "Network Mobility
Route Optimization Requirements for Operational Use in
Aeronautics and Space Exploration Mobile Networks",
RFC 5522, October 2009.
[RFC5720] Templin, F., "Routing and Addressing in Networks with
Global Enterprise Recursion (RANGER)", RFC 5720,
February 2010.
[RFC5743] Falk, A., "Definition of an Internet Research Task Force
(IRTF) Document Stream", RFC 5743, December 2009.
[RFC5887] Carpenter, B., Atkinson, R., and H. Flinck, "Renumbering
Still Needs Work", RFC 5887, May 2010.
[RFC6115] Li, T., "Recommendation for a Routing Architecture",
RFC 6115, February 2011.
[RFC6139] Russert, S., Fleischman, E., and F. Templin, "Routing and
Addressing in Networks with Global Enterprise Recursion
(RANGER) Scenarios", RFC 6139, February 2011.
[RFC6169] Krishnan, S., Thaler, D., and J. Hoagland, "Security
Concerns with IP Tunneling", RFC 6169, April 2011.
[RFC6740] Atkinson,, RJ., "Identifier-Locator Network Protocol
(ILNP) Architectural Description", RFC 6740,
November 2012.
[RFC6830] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The
Locator/ID Separation Protocol (LISP)", RFC 6830,
January 2013.
[RO-CR] Bernardos, C., Calderon, M., and I. Soto, "Correspondent
Router based Route Optimisation for NEMO (CRON)", Work
in Progress, July 2008.
[SAMPLE] Carpenter, B. and S. Jiang, "Legacy NAT Traversal for
IPv6: Simple Address Mapping for Premises Legacy Equipment
(SAMPLE)", Work in Progress, June 2010.
[TTRMOB] Whittle, R. and S. Russert, "TTR Mobility Extensions for
Core-Edge Separation Solutions to the Internet's Routing
Scaling Problem,
http://www.firstpr.com.au/ip/ivip/TTR-Mobility.pdf",
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August 2008.
Appendix A. IRON Operation over Internetworks with Different Address
Families
The IRON architecture leverages the routing system by providing
generally shortest-path routing for packets with CPA addresses from
APs that match the address family of the underlying Internetwork.
When the APs are of an address family that is not routable within the
underlying Internetwork, however, (e.g., when OSI/NSAP [RFC0994] APs
are used over an IPv4 Internetwork) a global Master AP mapping
database (MAP) is required. The MAP allows the Relays of the local
IRON instance to map APs belonging to other IRON instances to
addresses taken from companion prefixes of address families that are
routable within the Internetwork. For example, an IPv6 AP (e.g.,
2001:DB8::/32) could be paired with one or more companion IPv4
prefixes (e.g., 192.0.2.0/24) so that encapsulated IPv6 packets can
be forwarded over IPv4-only Internetworks. (In the limiting case,
the companion prefixes could themselves be singleton addresses, e.g.,
192.0.2.1/32).
The MAP is maintained by a globally managed authority, e.g. in the
same manner as the Internet Assigned Numbers Authority (IANA)
currently maintains the master list of all top-level IPv4 and IPv6
delegations. The MAP can be replicated across multiple servers for
load balancing using common Internetworking server hierarchies, e.g.,
the DNS caching resolvers, ftp mirror servers, etc.
Upon startup, each Relay advertises IPv4 companion prefixes (e.g.,
192.0.2.0/24) into the IPv4 Internetwork routing system and/or IPv6
companion prefixes (e.g., 2001:DB8::/64) into the IPv6 Internetwork
routing system for the IRON instance that it serves. The Relay then
selects singleton host numbers within the IPv4 companion prefixes
(e.g., 192.0.2.1) and/or IPv6 companion prefixes (e.g., as
2001:DB8::0), and assigns the resulting addresses to its Internetwork
interfaces. (When singleton companion prefixes are used (e.g.,
192.0.2.1/32), the Relay does not advertise a the companion prefixes
but instead simply assigns them to its Internetwork interfaces and
allows standard Internet routing to direct packets to the
interfaces.)
The Relay then discovers the APs for other IRON instances by reading
the MAP, either a priori or on-demand of data packets addressed to
other AP destinations. The Relay reads the MAP from a nearby MAP
server and periodically checks the server for deltas since the
database was last read. The Relay can then forward packets toward
CPAs belonging to other IRON instances by encapsulating them in an
outer header of the companion prefix address family and using the
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Relay anycast address as the outer destination address.
Appendix B. Scaling Considerations
Scaling aspects of the IRON architecture have strong implications for
its applicability in practical deployments. Scaling must be
considered along multiple vectors, including interdomain core routing
scaling, scaling to accommodate large numbers of EUNs, traffic
scaling, state requirements, etc.
In terms of routing scaling, each VSP will advertise one or more APs
into the interdomain routing system from which CPs are delegated to
end users. Routing scaling will therefore be minimized when each AP
covers many CPs. For example, the IPv6 prefix 2001:DB8::/32 contains
2^24 ::/56 CP prefixes for assignment to EUNs; therefore, the VSP
could accommodate 2^32 ::/56 CPs with only 2^8 ::/32 APs advertised
in the interdomain routing core. (When even longer CP prefixes are
used, e.g., /64s assigned to individual handsets in a cellular
provider network, many more EUNs can be represented within only a
single AP.)
In terms of traffic scaling for Relays, each Relay represents an ASBR
of a "shell" enterprise network that simply directs arriving traffic
packets with CPA destination addresses towards Servers that service
the corresponding Clients. Moreover, the Relay sheds traffic
destined to CPAs through redirection, which removes it from the path
for the majority of traffic packets between Clients within the same
IRON instance. On the other hand, each Relay must handle all traffic
packets forwarded between the CPs it manages and the rest of the
Internetwork. The scaling concerns for this latter class of traffic
are no different than for ASBR routers that connect large enterprise
networks to the Internet. In terms of traffic scaling for Servers,
each Server services a set of CPs. The Server services all traffic
packets destined to its own CPs but only services the initial packets
of flows initiated from its own CPs and destined to other CPs.
Therefore, traffic scaling for CPA-addressed traffic is an asymmetric
consideration and is proportional to the number of CPs each Server
serves. When possible, the Server can also be removed from the path
in order to allow direct Client-to-Client communications as described
in Section 8.1.3. In that case, the Server's burden in handling data
packets is greatly reduced.
In terms of state requirements for Relays, each Relay maintains a
list of Servers in the IRON instance as well as forwarding table
entries for the CPs that each Server handles. This Relay state is
therefore dominated by the total number of CPs handled by the Relay's
associated Servers. Keeping in mind that current day core router
technologies are only capable of handling fast-path FIB cache sizes
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of O(1M) entries, a large-scale deployment may require that the total
CP database for the VSP overlay be spread between the FIBs of a mesh
of Relays rather than fully-resident in the FIB of each Relay. In
that case, the techniques of Virtual Aggregation (VA) may be useful
in bridging together the mesh of Relays. Alternatively, each Relay
could elect to keep some or all CP prefixes out of the FIB and
maintain them only in a slow-path forwarding table. In that case,
considerably more CP entries could be kept in each Relay at the cost
of incurring slow-path processing for the initial packets of a flow.
In terms of state requirements for Servers, each Server maintains
state only for the CPs it serves, and not for the CPs handled by
other Servers in the IRON instance. Finally, neither Relays nor
Servers need keep state for final destinations of outbound traffic.
Clients source and sink all traffic packets originating from or
destined to the CP. Therefore, traffic scaling considerations for
Clients are the same as for any site border router. Clients also
retain tunnel neighbor state for final destinations of outbound
traffic flows. This can be managed as soft state, since stale
entries purged from the cache will be refreshed when new traffic
packets are sent.
Author's Address
Fred L. Templin (editor)
Boeing Research & Technology
P.O. Box 3707 MC 7L-49
Seattle, WA 98124
USA
EMail: fltemplin@acm.org
Templin Expires September 29, 2014 [Page 41]
